import java.util.Random;

public class TestNum {
    public  static  String getCharAndNumr(int length)
    {
        String val = "";
        Random random = new Random();
        for(int i = 0; i < length; i++)
        {
            String charOrNum = random.nextInt(2) % 2 == 0 ? "char" : "num"; // 输出字母还是数字

            if("char".equalsIgnoreCase(charOrNum)) // 字符串
            {
                int choice =65; //取得大写字母还是小写字母
                val += (char) (choice + random.nextInt(26));
            }
            else if("num".equalsIgnoreCase(charOrNum)) // 数字
            {
                val += String.valueOf(random.nextInt(10));
            }
        }
        return val;
    }

    public static void main(String[] args) {
        getCharAndNumr(16);
        System.out.println(getCharAndNumr(16));
        System.out.println(getCharAndNumr(16));
        System.out.println(getCharAndNumr(16));
    }
}
